EEPROM: Use constant instead of a hardcoded value for uninitialized bytes

Instead of hardcoding 255 in the `eeprom.erase` handler, use a constant instead,
to make it clear what the number is.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

plugins/Kaleidoscope-EEPROM-Settings/src/kaleidoscope/plugin/EEPROM-Settings.cpp

@@ -246,7 +246,7 @@ EventHandlerResult FocusEEPROMCommand::onFocusEvent(const char *command) {
     break;
   case ERASE: {
     for (uint16_t i = 0; i < Runtime.storage().length(); i++) {
-      Runtime.storage().update(i, 255);
+      Runtime.storage().update(i, EEPROM_UNINITIALIZED_BYTE);
     }
     Runtime.storage().commit();
     Runtime.device().rebootBootloader();

plugins/Kaleidoscope-EEPROM-Settings/src/kaleidoscope/plugin/EEPROM-Settings.h

@@ -28,9 +28,12 @@ class EEPROMSettings : public kaleidoscope::Plugin {
   EventHandlerResult onSetup();
   EventHandlerResult beforeEachCycle();
 
+  /* EEPROM is filled with 0xff when uninitialized, and we use that in a few
+   * places. */
+  static constexpr uint8_t EEPROM_UNINITIALIZED_BYTE = 0xff;
   /* EEPROM is filled with 0xff when uninitialized, so a version with that value
    * means we do not have an EEPROM version defined yet. */
-  static constexpr uint8_t VERSION_UNDEFINED = 0xff;
+  static constexpr uint8_t VERSION_UNDEFINED = EEPROM_UNINITIALIZED_BYTE;
   /* A version set to zero is likely some kind of corruption, we do not normally
    * clear the byte. */
   static constexpr uint8_t VERSION_IMPOSSIBLE_ZERO = 0x00;